WASHINGTON—There is little doubt the Supreme Court will extend its turn to the right if Judge Brett Kavanaugh joins the bench this fall. But Judge Kavanaugh’s connection with nearly every justice, and his reputation as a straight-shooter even among those who disagree with him, suggests he would make the ride as smooth as possible.

The court’s last term saw it swerve between far-reaching 5-4 decisions that overruled precedent and cases that fizzled out with procedural rulings. The next justice’s demeanor could calm an institution no longer entirely immune to the discord that now defines Washington.

“They say every time you get a new justice, the whole chemistry of the court changes,” said Daniel Epps, a law professor at Washington University in St. Louis.

This time, there won’t simply be a change in personality, but in the court’s ideological cast if Judge Kavanaugh, a down-the-line conservative, succeeds Justice Anthony Kennedy, a Ronald Reagan appointee who found accommodation with liberals in decisions expanding gay rights, maintaining access to abortion, and limiting capital punishment.

Over 12 years on the U.S. Court of Appeals for the District of Columbia Circuit, Judge Kavanaugh has built “a very good reputation for working with people across ideological lines,” Mr. Epps says, and the clerks he has sent to the Supreme Court have been hired by justices of every ideological bent.

The U.S. Supreme Court, seen in the official group portrait in June 2017, could see a shift in the tone of its discourse if Judge Kavanaugh is confirmed to succeed Jusice Anthony Kennedy, seated, second from left.
Photo:
J. Scott Applewhite/Associated Press

Last term alone, former Kavanaugh clerks worked for Chief Justice John Roberts and Justices Kennedy, Samuel Alito and Elena Kagan. Justices Stephen Breyer and Neil Gorsuch each have hired a Kavanaugh clerk for the new term that begins in October.

In several recent years Judge Kavanaugh has joined with Justice Ruth Bader Ginsburg and other Democratic appointees for mock trials staged by Washington’s Shakespeare Theatre Company.

Judge Kavanaugh took pains to praise another liberal judge, Robert Katzmann of the Second Circuit in New York, when reviewing his book, “Judging Statutes,” which advanced legal methods at odds with his own.

Related Video

When the Supreme Court’s fall term begins in October, justices will hear cases that could impact the criminal justice system, major tech companies and charities. WSJ’s Shelby Holliday looks at key cases on the docket. Photo: AP.

“Chief Judge Katzmann is one of America’s finest judges and a true role model for me and many others, both in how he approaches his job and in how he seeks to improve the system of justice,” Judge Kavanaugh wrote two years ago in the Harvard Law Review. “Even where I disagree, I have learned a great deal.”

In response, Chief Judge Katzmann wrote, “I could not have hoped for a more thoughtful examination of the subject.”

Should he join the Supreme Court, Judge Kavanaugh “already has built-in relationships. He’s a voice the justices are going to be primed to listen to,” said Luke McCloud, a lawyer at Williams & Connolly LLP who clerked for Judge Kavanaugh before clerking for Justice Sonia Sotomayor.

Mr. McCloud said that on the D.C. Circuit, Judge Kavanaugh “always tried to take his colleagues’ views into account even when he disagreed with them.”

It is hard to know how collegiality translates into judicial decisions, but there have been times when Judge Kavanaugh has found himself in the majority when fellow conservatives dissented.

In 2013, he was in the majority of a 2-1 ruling that sided with environmentalists in a greenhouse gas case over regulation of “biogenic” emissions. In 2014, he was part of the majority when the full court upheld government regulations that required country-of-origin labeling on meat products, over a dissent by other conservatives who believed the First Amendment prohibited the compelled disclosures.

Judge Kavanaugh “doesn’t have any sharp elbows,” said Carter Phillips of Sidley Austin LLP, who has argued numerous cases at the D.C. Circuit and the Supreme Court. “He’s nice to everybody in every setting I’ve seen him.”

It was by no means evident that Judge Kavanaugh would win plaudits for collegiality when President George W. Bushnominated him to the D.C. Circuit in 2003.

At that point, Judge Kavanaugh was best known as a combatant in the partisan wars that raged from Bill Clinton’s presidency through the disputed 2000 presidential election and into the Bush administration. He had served as a top prosecutor in the Whitewater investigation that led to Mr. Clinton’s impeachment.

Judge Kavanaugh helped the legal team that put Mr. Bush in the White House after a Florida election recount was halted. Under then-White House Counsel Alberto Gonzales, Judge Kavanaugh helped drive the Bush administration’s push to put young conservatives on the federal bench, including Chief Justice Roberts, whom he counts as a friend.

“Brett Kavanaugh’s nomination to the D.C. Circuit is not just a drop of salt in the partisan wounds,” Sen. Chuck Schumer (D., N.Y.), now the Senate minority leader, said in 2004. “It’s the whole shaker.”

When Mr. Trump announced his nomination this month, Judge Kavanaugh tried to show that times had changed. He thanked Justice Kagan, a 2010 Barack Obama appointee, for hiring him to teach a course when she was dean of Harvard Law School.

The Kavanaugh-Kagan relationship may be one to watch in particular, should they serve together. As her offer—and his acceptance—to teach at Harvard suggests, both have seen advantage in detente.

That could create a contrast with Justice Gorsuch, whose first term suggests little collaboration with liberal colleagues. “It will be interesting to see if [Kagan] and Kavanaugh forge some kind of relationship that seems to be absent with Justice Gorsuch,” Mr. Epps said.

Justice Gorsuch had a similar reputation for collegiality, “and then it seemed less true when he got to the Supreme Court,” Mr. Epps said. Justice Gorsuch’s arrival was followed by a strain on the court, many court watchers have noted, including rocky moments at oral argument and an unusually long time to resolve cases.

While much has been made of the Supreme Court’s division into solid conservative and liberal camps, the court in recent years has sometimes featured four distinct camps instead of two.

On the far right are Justices Clarence Thomas and Alito, and Justice Gorsuch in his early tenure has often joined them. Justices Ginsburg and Sotomayor have provided almost a mirror image on the left, voicing stronger positions in several hot-button cases than their fellow liberals.

Meanwhile, Chief Justice Roberts and Justice Kennedy on occasion have served as bridge builders from the right, at times making accommodations with Justices Breyer and Kagan from the left. On the circuit court, Judge Kavanaugh appeared closer to that center, at least in temperament.

That could lead to smoother functioning of the institution, where—despite where most of the attention often focuses—most of the caseload doesn’t involve controversial social or political issues.

But however pleasant it may for liberals be to work alongside Judge Kavanaugh, any compromise or give-and-take would be limited to less consequential cases. As Mr. Epps put it, “Being nice is not going to get a justice to vote to overturn Roe v. Wade if they wouldn’t otherwise.”